The proposed research is aimed at directly examining the factors that control the activity of serotonin-containing neurons in the mammalian CNS and the functional role of these neurons. The studies will utilize electrophysiological techniques (unit activity in freely moving cats and anesthetized rats), pharmacological methods, autoradiography, and receptor binding studies. Additional studies will utilize the horse-radish peroxidase method for tracing both the afferents and efferents of this neurochemically identifiable neuron system.